Data Communications in a Distributed Computing Environment

1. A method of data communications in a distributed computing environment, the distributed computing environment including a plurality of computers coupled for data communications through communications adapters and an active messaging interface (‘AMI’), the method comprising: issuing, by a sender to a receiver, an eager SEND data communications instruction to transfer SEND data, the instruction including information describing data location at the sender and data size; transmitting, by the sender to the receiver, the SEND data as eager data packets; initially discarding, by the receiver based on data flow conditions, the eager data packets as they are received from the sender; subsequently accepting by the receiver, based on the data flow conditions, undiscarded eager data packets upon receipt from the sender; and transferring, based on the data flow conditions, by the receiver from the sender's data location to a receive buffer by remote direct memory access (“RDMA”), the SEND data of the discarded packets.

2. The method of claim 1 wherein the data flow conditions comprise availability of temporary buffer space for the eager data packets.

3. The method of claim 1 wherein the data flow conditions comprise availability in the receiver of a RECEIVE instruction corresponding to the eager SEND instruction, the RECEIVE instruction including the memory location of a receive buffer.

4. The method of claim 1 wherein discarding the eager data packets is carried out with no utilization of an eager protocol limit, the eager protocol limit comprising a data size above which a sender selects a rendezvous protocol instead of an eager protocol for transmission of data.

5. The method of claim 1 wherein discarding the eager data packets is carried out with no utilization of any flow control token or flow control accounting.

6. An apparatus for data communications in a distributed computing environment, the distributed computing environment including a plurality of computers coupled for data communications through communications adapters and an active messaging interface (‘AMI’), the computers comprising computer processors operatively coupled to computer memory having disposed within it computer program instructions that, when executed by the computer processors, cause the computers in the distributed computing environment to carry out the steps of: issuing, by a sender to a receiver, an eager SEND data communications instruction to transfer SEND data, the instruction including information describing data location at the sender and data size; transmitting, by the sender to the receiver, the SEND data as eager data packets; initially discarding, by the receiver based on data flow conditions, the eager data packets as they are received from the sender; subsequently accepting by the receiver, based on the data flow conditions, undiscarded eager data packets upon receipt from the sender; and transferring, based on the data flow conditions, by the receiver from the sender's data location to a receive buffer by remote direct memory access (“RDMA”), the SEND data of the discarded packets.

7. The apparatus of claim 6 wherein the data flow conditions comprise availability of temporary buffer space for the eager data packets.

8. The apparatus of claim 6 wherein the data flow conditions comprise availability in the receiver of a RECEIVE instruction corresponding to the eager SEND instruction, the RECEIVE instruction including the memory location of a receive buffer.

9. The apparatus of claim 6 wherein discarding the eager data packets is carried out with no utilization of an eager protocol limit, the eager protocol limit comprising a data size above which a sender selects a rendezvous protocol instead of an eager protocol for transmission of data.

10. The apparatus of claim 6 wherein discarding the eager data packets is carried out with no utilization of any flow control token or flow control accounting.

11. A computer program product for data communications in a distributed computing environment, the distributed computing environment including a plurality of computers coupled for data communications through communications adapters and an active messaging interface (‘AMI’), the computer program product disposed upon a non-transitory computer readable storage medium, the computer program product comprising computer program instructions that, when installed and executed, cause the parallel computer to carry out the steps of: issuing, by a sender to a receiver, an eager SEND data communications instruction to transfer SEND data, the instruction including information describing data location at the sender and data size; transmitting, by the sender to the receiver, the SEND data as eager data packets; initially discarding, by the receiver based on data flow conditions, the eager data packets as they are received from the sender; subsequently accepting by the receiver, based on the data flow conditions, undiscarded eager data packets upon receipt from the sender; and transferring, based on the data flow conditions, by the receiver from the sender's data location to a receive buffer by remote direct memory access (“RDMA”), the SEND data of the discarded packets.

12. The computer program product of claim 11 wherein the data flow conditions comprise availability of temporary buffer space for the eager data packets.

13. The computer program product of claim 11 wherein the data flow conditions comprise availability in the receiver of a RECEIVE instruction corresponding to the eager SEND instruction, the RECEIVE instruction including the memory location of a receive buffer.

14. The computer program product of claim 11 wherein discarding the eager data packets is carried out with no utilization of an eager protocol limit, the eager protocol limit comprising a data size above which a sender selects a rendezvous protocol instead of an eager protocol for transmission of data.

15. The computer program product of claim 11 wherein discarding the eager data packets is carried out with no utilization of any flow control token or flow control accounting.